Inflammatory Bowel disease (IBD) which gathers Crohn's disease (CD) and Ulcerative Colitis (UC) affects 1.4 million Americans and the prevalence rate is 396 per 100 000 individuals worldwide. Incidence and prevalence are increasing in various regions of the world including the ones which were less impacted.
Due to its symptoms (diarrhea, abdominal pain, loss of weigh), IBD is considered as an incapacitating disease. Patients have a higher risk factor to develop other inflammatory or non-inflammatory disorders like psoriasis, cancer or arthritis. So far no curative treatments exist for the disease. The most powerful treatment is the injection of the recombinant antibodies targeting TNF-α (infliximab), however even if 60% are primary responders this drops to 25-40% still in remission after one year of treatment. The last solution in IBD is surgery where inflamed parts of the intestine are withdrawn. However surgery can lead to severe complications as Short Bowel syndrome and relapses are frequent. All together, this makes IBD one of the major health problems in developed country and the development of innovative therapeutics or curative strategies is crucial.
One of the ways explored to help in alleviating symptoms of the disease is the delivery of anti-inflammatory molecules by recombinant lactic acid bacteria (LAB). Recently, it has been shown that mice fed with LAB expressing the protease inhibitor Elafin were protected against gut inflammation. LAB have been used for thousand years for food conservation and appear to be a promising vehicle delivering active molecules. They are recognized as safe by World Health Organization, and some strains can have anti-inflammatory properties.
Lactococcus lactis is the most widely used Lactic Acid Bacterium (LAB) in the production of fermented milk products and is considered as the model LAB because many genetic tools have been developed and its complete genome has been completely sequenced (Bolotin, Wincker et al. 2001, Genome Res, 11, 731-753). Thus, this food-grade Gram-positive bacterium represents a good candidate to produce and deliver therapeutic proteins to the mucosal immune system. In the last decade, the potential of live recombinant lactococci to deliver such proteins to the mucosal immune system has been widely investigated (Steidler, Robinson et al. 1998, Infect Immun, 66, 3183-3189; Bermudez-Humaran, Cortes-Perez et al. 2004, J Med Microbiol, 53, 427-433; Hanniffy, Wiedermann et al. 2004, Adv Appl Microbiol, 56, 1-64; Wells and Mercenier 2008, Nat Rev Microbiol, 6, 349-362; Bermudez-Humaran, Kharrat et al. 2011, Microb Cell Fact, 10 suppl 1, S4). This approach offers several advantages over the traditional systemic injection, such as easy administration and the ability to elicit both systemic and mucosal immune responses (Mielcarek, Alonso et al. 2001, Adv Drug Deliv Rev, 51, 55-69; Eriksson and Holmgren 2002, Curr Opin Immunol, 14, 666-672).
Initial studies on the use of L. lactis secreting biologically active molecules were performed with murine interleukin-2 (IL-2, a pro-inflammatory cytokine) (Steidler, Robinson et al. 1998, supra). The encouraging data obtained in this pioneer work stimulated researchers to further investigate whether mucosal and systemic responses could be enhanced by co-expression (and secretion) of either mulL-2 or mulL-6 (another pro-inflammatory cytokine) with the model antigen Tetanus Toxin Fragment C (TTFC) (Steidler, Robinson et al. 1998, supra). Compared to mice immunized with a TTFC-expressing strain of L. lactis, the anti-TTFC serum responses peak was 10-15-fold higher in mice co-immunized with the TTFC-expressing L. lactis strain and L. lactis expressing either mulL-2 or mulL-6. This was the first demonstration that biologically active cytokines could be delivered to the mucosa using LAB. Then, the laboratory reported a L. lactis strain able to deliver in situ biologically active mulL-12 (LL-mulL12) at mucosal surfaces (eg. airway or digestive mucosa). IL-12 is a potent pleiotropic cytokine that induces T helper 1 (TH1) cells and interferon-γ (IFN-γ) production, enhances cytotoxic T lymphocyte (CTL) maturation, promotes natural killer (NK) cell activity and possesses adjuvant properties when co-delivered with vaccinal antigens. Particularly, we used 3 models where LL-mull-12 was successfully used: (1) as an adjuvant in the context of mucosal vaccination against Human Papillomavirus type-16 (HPV-16) (Bermudez-Humaran, Langella et al. 2003, Infect Immun, 71, 1887-1896; Bermudez-Humaran, Cortes-Perez et al. 2004, supra; Adel-Patient, Ah-Leung et al. 2005, Cin Exp Allergy, 35, 539-546), (2) to modulate TH1/TH2 balance in an ovalbumin (OVA)-induced asthma model (Wu, Yang et al. 2006, Int Immunopharmacol 6, 610-615) and (3) to prevent an allergic reaction against the cow's milk allergen β-lactoglobulin (BLG) (Adel-Patient, Ah-Leung et al. 2005, supra; Cortes-Perez, Ah-Leung et al. 2007, Clin Vaccine Immunol 14, 226-233).
However, there is still a strong need of new LAB which could be used as anti-inflammatory agent.